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Strong Field Dynamics of Bosonic Fields

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Strong Field Dynamics of Bosonic Fields Strong field dynamics of bosonic fields: Looking for new particles and modified gravity William East, Perimeter Institute ICERM Workshop October 26, 2020 ... Introduction How can we use gravitational waves to look for new matter? Can we come up with alternative predictions for black holes and/or GR to test against observations? Need understanding of relativistic/nonlinear dynamics for maximum return William East Strong field dynamics of bosonic fields ... Three examples with bosonic fields Black hole superradiance, boson stars, and modified gravity with non-minially coupled scalar fields William East Strong field dynamics of bosonic fields ... Gravitational wave probe of new particles Search new part of parameter space: ultralight particles weakly coupled to standard model William East Strong field dynamics of bosonic fields ... Superradiant instability: realizing the black hole bomb Massive bosons (scalar and vector) can form bound states, when frequency ! < mΩH grow exponentially in time. Search for new ultralight bosonic particles (axions, dark massive “photons," etc.) with Compton wavelength comparable to black hole radius (Arvanitaki et al.) William East Strong field dynamics of bosonic fields ... Boson clouds emit gravitational waves WE (2018) William East Strong field dynamics of bosonic fields ... Boson clouds emit gravitational waves 50 100 500 1000 5000 104 107 Can do targeted 105 1000 searches–e.g. follow-up 10 0.100 black hole merger events, 0.001 1 or “blind" searches 0.8 0.6 Look for either resolved or 0.4 1 stochastic sources with 0.98 0.96 LIGO (Baryakthar+ 2017; 0.94 Zhu+ 2020; Brito+ 2017; 10-12 10-11 10-10 Tsukada+ 2019) Siemonsen & WE (2020) William East Strong field dynamics of bosonic fields ... Stochastic gravitational wave background Can already place constraints on vector bosons with LIGO O1+O2 (with moderate assumptions on black hole spin) Tsukada, Brito, WE, & Siemonsen (in prep.) William East Strong field dynamics of bosonic fields ... Testing the black hole paradigm Black hole seems to fit. But are there horizonless objects that can give similar behavior? Caltech/MIT/LIGO Lab William East Strong field dynamics of bosonic fields ... Boson stars Are easy to evolve (c.f. gravastars, constant density stars, etc.). Can be ultracompact. Can be rapidly spinning. Can have stable photon orbits, ergospheres, etc. But are they stable? 101 0.4 101 0.3 0 2 10 − µM 0.2 M/R Repulsive JM Mini KKLS 100 0.1 1 Solitonic 10− Axionic 0.0 0.00 0.25 0.50 0.75 1.00 0.00 0.25 0.50 0.75 1.00 0.00 0.25 0.50 0.75 1.00 ω/µ ω/µ ω/µ Siemonsen & WE (in prep.) William East Strong field dynamics of bosonic fields ... Rotating boson star stability Maybe not. Palenzuela et al. (2017) Also Sanchis-Gual et al. (2019): Rotating stars are unstable for massive scalar bosons; Rotating massive vector stars are more stable. (See J. Font’s talk) William East Strong field dynamics of bosonic fields ... Boson stars Use 3D full GR evolutions to study stability of complex scalar 0 0 boson stars with nonlinear interactions, Φ = V (Φ) with V nonlinear. 3.0 Repulsive 2.5 Mass Term KKLS 2.0 Solitonic 2 /µ Axionic (40 ) ) | × 1.5 Φ | ( V 1.0 0.5 0.0 0.00 0.25 0.50 0.75 1.00 1.25 1.50 Φ | | Nils Siemonsen & WE (in prep.) William East Strong field dynamics of bosonic fields ... Non-axisymmetric instability Example of rotating axionic boson star William East Strong field dynamics of bosonic fields ... Unstable and stable boson stars 1 10− KKLS Solitonic I Axionic ˜ ω M 2 10− 0.4 0.5 0.6 0.7 0.8 1 10− R ˜ ω M 2 10− 0.4 0.5 0.6 0.7 0.8 ω/µ With nonlinear coupling, instability shuts off in relativistic regime for some cases. Siemonsen & WE (in prep.) William East Strong field dynamics of bosonic fields ... Boson stars: outlook 1 KKLS 10− Solitonic Axionic Repulsive 4 10− m Mini Φ 7 10− 0 2000 4000 6000 8000 10000 12000 t/M Siemonsen & WE (in prep.) Class of rotating scalar boson stars stable on long timescales Can study mergers of these as point of comparison to black holes. Longer timescale instabilities (e.g. ergoregion, light ring, etc.)? William East Strong field dynamics of bosonic fields ... Modifying general relativity 1 Z 1 1 S = d 4xp g( R ( φ)2 V (φ) + α (φ)( φ)4 + β (φ) 8π − 2 − 2 r − r G ∗ abcd abcd 2 6 + γ (φ) R Rabcd + (R Rabcd ) =Λ + :::) Some modifications no longer have 2nd order equations of motion In that case one has no choice but to use order-reduction (see M. Okounkova’s talk) or modify short wavelength behavior (e.g. Cayuso & Lehner, 2020) For those with 2nd order equations (Horndeski theories) may be well-posed, but usually aren’t in commonly used formulations (Papallo & Reall). William East Strong field dynamics of bosonic fields ... Modification to generalized harmonic — Kovacs & Reall (2020) Introduce auxiliary metrics that determine gauge and constraint propagation. Equations of motion will still be strongly hyperbolic for Horndeski theories with λ L2. William East Strong field dynamics of bosonic fields ... Non-perturbative dynamics of Horndeski Can we get this to work strong-field/dynamical systems (e.g. black hole mergers) and non-negligible coupling? (Work with Justin Ripley) Focus on Einstein-dilaton Gauss Bonnet 1 Z 1 1 S = d 4xp g R ( φ)2 + λφ 8π − 2 − 2 r G Representative example of Horndeski, violates null convergence condition Can leverage experience regarding hyperbolicity in spherically symmetric case (Ripley & Pretorius) See also Helvi Witek’s talk in previous workshop for test field case. William East Strong field dynamics of bosonic fields ... EDGB equations in modified harmonic Evolution variables g ;@t g ; φ, @t φ f ab ab g ! A ef B g F (g) ab ab @2 ef + ab = 0 Cef D t φ F (φ) with gauge choices Ha; g~ ; g^ . f ab abg In modified harmonic formulation, principal matrix no ef longer diagonal. In Horndeski, C and Bab non-zero, and matrix involves second-derivatives. Carry over experience with constraint damping, gauge conditions, from generalized harmonic. Black hole excision essential. William East Strong field dynamics of bosonic fields ... Improved hyperbolicity Harmonic vs. auxiliary metric harmonic 2.0 2.0 || h/L = 1/128 h/L = 1/1024 || h/L = 1/128 h/L = 1/1024 h/L = 1/256 h/L = 1/2048 h/L = 1/256 h/L = 1/2048 = 0) = 0) t 1.5 h/L = 1/512 t 1.5 h/L = 1/512 ( ( h h ab ab g g 0 0 ∂ 2 ∂ 2 || λ/L = 0.025 || λ/L = 0.025 / 1.0 / 1.0 || ˜ ˆ || ˜ ˆ ) A = 0.0, A = 0.0 ) A = 0.2, A = 0.4 t t ( ( h h ab ab g g 0 0.5 0 0.5 ∂ ∂ || || 0.0 0.0 0 1 2 3 4 5 0 1 2 3 4 5 t/L t/L Use of auxiliary metrics removes frequency dependence growth. WE & Ripley in prep. William East Strong field dynamics of bosonic fields ... Black hole collisions 0.5 1.04 2 2 λ/m2 = 0.05 λ/m = 0.00 λ/m = 0.15 λ/m2 = 0.05 λ/m2 = 0.18 0.4 2 1.02 λ/m = 0.10 λ/m2 = 0.10 λ/m2 = 0.15 0.3 1.00 2 /M AH λ/m = 0.18 i AH φ h 0.2 M 0.98 Σ 0.1 0.96 0.0 0.94 0 50 100 150 200 250 300 350 0 50 100 150 200 250 t/M t/M Black holes scalarize while shrinking, and then collide. WE & Ripley in prep. William East Strong field dynamics of bosonic fields ... Black hole collisions: radiation 4 4 10 10− 1.2 × − 1.0 × λ/m2 = 0.05 λ/m2 = 0.00 1.0 λ/m2 = 0.10 0.8 λ/m2 = 0.05 λ/m2 = 0.15 λ/m2 = 0.10 2 ) 0.8 2 λ/m2 = 0.18 λ/m2 = 0.15 18 . 0.6 0 2 λ/m λ/m = 0.18 ( 0.6 GW P × 0.4 SF ˙ 0.4 E 0.2 0.2 0.0 0.0 160 170 180 190 200 210 220 230 160 170 180 190 200 210 220 230 (t r)/M (t r)/M − − Scalar and gravitational wave radiation in full EDGB. WE & Ripley in prep. William East Strong field dynamics of bosonic fields ... Binary black hole inspiral To do: Determine domain where theories are well-posed, and can give predictions for GW observations (case-by-case). Compare to order-reduction, other approximations that may not capture secular/non-perturbative effects. William East Strong field dynamics of bosonic fields ... Conclusion Gravitational waves provide new probes of fundamental physics that may be inaccessible to terrestrial experiments. Place interesting constraints on new particles with current, upcoming observations Can use boson stars to test limits of horizonless compact objects Make non-perturbative predictions for modified gravity theories (and determine where this is possible) Understanding of detailed dynamics, targeted analyses important. William East Strong field dynamics of bosonic fields.
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